Networks for mobile telecommunications apparatuses are known. These networks are generally described as cellular and they are distinguished by a plurality of cells, each defined as the group of territorial points served by the radio-electric signal radiated by an antenna (radio interface).
Apart from the intrinsic mobility of users, the main peculiarity of networks of mobile apparatuses is the use of the radio interface as access port to the network itself.
It is also known that dimension and performance assessments of telecommunications networks or systems in which the traffic offered is composed of voice traffic only, are made by using a method at the basis of which is a model described as being of the M/M/N type where the first M stands for the exponential distribution of the calls offered by the system, the second M stands for the exponential distribution of the duration of the calls served and N corresponds to the number of lines, telephone channels or resources available, all this being expressed using what is known as the “Erlang-B” formula.
Using this method it is possible to determine dimensioning and/or performance in probabilistic terms or, in other words, the level of service P(c) of the telecommunications system examined, in the periods with the highest traffic (peak time), by means of the formula:
      P    ⁡          (      c      )        =                    ρ        c                    c        !                            ∑                  i          =          0                c            ⁢                          ⁢                        ρ          i                          i          !                    and in which:    λ is the number of calls arriving per unit of time:    μ is the number of calls served per unit of time:    C is the number of lines, telephone channels or resources available.
According to the state of the art, therefore, P(c) represents the percentage of incoming calls (or offers) not served (that is, blocked by the system) during the period of highest traffic (peak time) and is calculated on the basis of the telephone traffic offered and of the lines, telephone channels or resources available, naturally in the commonly known and accepted hypotheses that:
the number of incoming voice calls has a Poisson distribution with parameter λ, meaning, in an intuitive manner, that the distribution of the time between the instant of arrival of a call and the instant of arrival of the next call (inter-arrival time) is of the exponential type with parameter λ and, as a consequence, there are no bursts of calls;
the number of voice calls served has a distribution of the exponential type with parameter μ, meaning, in intuitive manner, that the distribution of the duration of the calls served by the system is of the exponential type with parameter μ.
The known method is indisputably adequate for assessing the dimensioning and performance of a telecommunications system of the type described and, as a consequence, of a base station (cell) of a mobile telephony system, such as GSM, which manages voice traffic only, as, in this case, the hypotheses indicated effectively provide a good approximation of reality.
It is also known that the assessment of the dimensioning and performance of telecommunications systems with voice traffic characterized by the presence of “queues”, because there are telephone exchanges for example, is carried out using methods at the basis of which is a model of the M/M/N/Q type in which the first three terms have the meanings already illustrated above and Q represents the number of calls awaiting service which can be queued in the system.
In general, these methods are characterised by the fact that they envisage a user “impatience” factor with a dropped call frequency parameter α.
However, the known methods mentioned so far are not suitable for managing data traffic, and even less, for mixed voice and data traffic and, as a consequence, cannot be used for assessing the dimensioning and performance of network base stations, of the GSM-GPRS type, for example.
As is known, in fact, a peculiarity of data or voice and data networks, such as GSM-GPRS networks, consists of the fact that networks of this type are suitable for supplying a multiplicity of “services” such as, for example, voice telephony, FTP, email and Internet access and that each of these service has, as a rule, different characteristics both in terms of speed (number of bits per second) and of traffic (volume to transmit, symmetry or asymmetry of the service). It follows from this that system cell dimensioning must take account jointly of the characteristics of each service and, in particular, of the coexistence of the traditional voice service and of the data services supported.
A first technical problem linked with the need to support data traffic consists of the fact that the data traffic transmission speed in these types of network and, more in general, in fixed data telephony networks, is not constant with time and greatly depends of the number of lines, telephone channels or resources available in a given instant.
In the specific case of the GSM-GPRS network, as is known, data traffic for the various types of service is managed (served) using radio carriers of predefined frequency and, in the framework of each radio carrier (FDMA access technique), by a given slot (the logic channel) among those periodically available in the framework of the time frame used on the radio interface (TDMA access technique). In this context, if even one user requests a data transmission, one whole slot of the GSM time frame is assigned to the user itself and this implies a given transmission speed, for example 9.05 kbit/s nominal, for the data encoding denominated CS-1, or 13.4 kbit/s nominal for the date encoding denominated CS-2. If, on the other hand, several users simultaneously request data transmission, the single slot is subdivided among the users themselves, with a consequent drop in the transmission speed which will therefore be a function of the number of active users in the system (cell) at that moment; in a more intuitive manner, the generic user notes a net data transmission speed which varies with time on the basis of the load conditions in the system itself. The characteristics of the phenomenon described are clearly different from those typical of simple voice-only transmission for which, as is known, the GSM time frame slot assigned to the user is attributed to the same in a univocal and exclusive manner until completion of the telephone call.
Therefore, the use of a method which has the Erlang-B formula as a basis, as found in the known state of the art, is found to be a very rough approximation of the results and in fact translates into a very approximate assessment of the dimensioning of a data management network, such as, for example, a GSM-GPRS network. A second problem found in the known state of the art consists of the fact that nevertheless, as a rule, data traffic does not need to be served immediately and can therefore be queued and apparently therefore be approximated to an M/M/N/Q model in which this traffic leaves the queue or is served (if a phone channel is freed in the meantime) or because of dropping out of the system (what is called the customer's “impatience” which models the terminal-cell combination here), such a M/M/N/Q model and corresponding method once again entails a rough approximation of the results as its does not envisage managing the traffic with resources which vary over time.
Therefore, the use of a method which has the Erlang-B formula as a basis, modified to take account of the fact that the data traffic can be queued, as found in the known state of the art, is found to be a very rough approximation of the results and in fact translates into a very approximate assessment of the dimensioning of a data and/or voice management network, such as, for example, the GSM-GPRS network.
A third problem present, in particular, in the case of co-existence of voice traffic and data traffic, resides in the fact that, as is known, to the extent that priority in these cases is given to voice traffic with respect to data traffic (preemption) in such a way as to attribute all the resources (or, in any case, all the resources placed in common between the two type of services) to the first type of traffic rather than to the second to which, at most, a minimum capacity protected from intrusion by voice calls is reserved, in this case to the state of the art known to date does not take account of this preemption, and, therefore, in assessing the performance of a mixed voice and data network, it substantially assesses performance as if voice and data did not coexist and there was no preemption.
It clearly emerges from the problems described so far, that the known methodologies for assessing dimensioning and performance of the base stations of a network for mobile telecommunications apparatuses are inadequate for the requirements and are such as to lead to rough assessment errors, as they do not take account of the peculiarities of data and/or voice and data traffic.